Safety device for machine tools



June 5, 1951 c. LARSEN SAFETY DEVICE FOR MACHINE TOOLS Filed March 4,1947 INVENTOR. CHRISTIAN LARSEN ATTORNEY Patented `lune 5, 1951 UNITEDSTATES PAT-ENT OFFICE 6 Claims.

amended April 30, 1928; 37.0y O. G. '757) Although the device of thisinvention is ofv more general application, the disclosed embodimentcomprises a grinding machine, particularly a machine of the type termeda bench grinder.

The operator of a bench grinder conventionally stands in front oftherotating abrasive wheel thereof, and he feeds the work to the wheelmanually. Particles of the piece and of the abrasive are thrown from thewheel, and there is danger that the operator will become injuredthereby. It is a purpose of the present invention to avoid such injuryto the operator.

The present application is a continuation in part of my co-pendingapplication, Serial No. 608,807, liled August 3, 1945 new abandoned.

The device of my co-pending application com'- prises a shield,specically in the form'oi a transparent panel, which is manuallypcsitionable into and out of guard position and operable when moved intoguard position to connect power to the abrasive wheel. Actuation oftheshield to connect the power places it in position between the' abrasivewheel and the operator, whereby it -protects the operator from flyingparticles.

The present invention comprises an abutment member, positioned where theoperator actuates it incident to operating the machine.' The' abutmentmember is actuated to complete connection of the abrasive wheel with itspower source and thereby power the machine, actuation of the abutmentmember being accomplished by the operator stationing himself to work themachine. In the case of the power source being an elecN tric motor, thepower-control means is a motor switch. A shield is provided similar tothe shield of my co-pending application hereinbefore referred to, whichoperates a line switch to connect the power source when it is moved intoguard position. The shield of the present invention carries the motorswitch, so positioned `that it is actuated by the operator automaticallyby the operator assuming his natural position for operating the machine,but the motor switch is out of position to be engaged by the operatorwhen the shield is up out of guard position.

When the operator discontinuos Working the machine, the circuit throughthe motor switch is automatically opened. If the operator inadvertentlytouches they abrasive wheel, he" instinctively jerks'away, and in doingso'heautof matically opens the motor switch and shuts off the power bythe act of disengaging the abutment member.

An electric light is also provided to illuminate the wheel, and a lightswitch is provided operable to be in closedV condition to illuminate thework whenever the'maehine isoperated.

A fuller understanding of the principles of the invention, and detailsofthe preferred 'embodiment disclosed, will be derived fromr theaccompanying drawings. In the` drawings;

Fig. l is a fragmentary side elevation of a bench grinder embodying thepresent invention, a portion thereof being a section taken on line l--lof Fig. 2; U

Fig. 2 is an elevation of the motor activating switch, the View beingupwardly in Figpjl; and

Fig. 3 is a wiring diagram of an electrical circuit for the invention.

The machine illustrated in Fig. l, to which the invention is applied,comprisesV a bench grinder, which includes one or more grinding wheelsIl, mounted to rotate with the shaft I2. Suitable power means areprovided to drive the shaft I2, such as the electric motor l5 indicatedin Fig. 3. In accordance with prior-art practice, the shaft l2 can bethe motor'shaft, which supports a grinding wheel or some other form ofabrasive or bufling wheel mounted on each of its ends. The structureappearing in Fig. 1, and described with reference to Fig. 1, is a singleabrasive wheel with its appurtenances. In practice there can be twosimilar structures mounted at opposite ends of the shaft I2.

A line switch It, mounted on a stationary portion ofthe machine, forexample on the wheel guard l'i, is positioned for operation' by theshield I3 to connect the power source'. The' line switch can be the sameas is disclosed in'the hereinbefore referred to cro-pending application,Serial No. 608,807. The preferred embodiment shown comprises a switchhousing i9, supported by the bracket 2B, mounted on the wheel guard Il.Fixed terminals 2| are provided, preferably of theopposed-spring-contact type, and the conn tact member 22 is movable intoand Yout of engagement with the terminals 2|. The contact member 22 isattached to the plunger 23 which is slidable longitudinally in theguides 24 and 25 in the end walls of the housing i9. The plunger 23 issprincr actuated by compression spring 26 to move the contact member 22out of engagement with the terminals 2|.

The shield I8 is supportedV by the bracket 38 which isv mounted ontheguard Il. Theshield comprises a panel 3| of glass or other suitablematerial, and is mounted to pivot at 32, its movement being downwardlyinto guard position and upwardly to idle position. At one end the panel3| carries an abutment shoe 33, which is positioned to engage andactuate the plunger 23 against the action of the spring 25 whenever theshield 3 is moved into its lower guard position.

The light 34 is preferably provided to illuminate the work and the wheelwhen the machine tool is being used. The light 34 can be mounted in anysuitable manner, for example as shown on the bracket 39, and the lightshield 35 can be provided as shown.

The shield 3| carries the motor switch 39 at its forward end. The switch38 embodies the abutment member 39, which is positioned where it isengaged by the body or torso of the operator when he naturally stationshimself to operate the machine.

The abutment number 39 is mounted to slide in the frame 43, preferablyformed integral with the forward edge of the panel 3|, the abutmentmember being projected to its outermost position by the springs 4|, andheld positioned by the locating pins 42 which ride in the guideways 43.

Attached to the abutment member 39 to move therewith is the electricalcontact 44 which, in the disclosed embodiment, is fixed to thedielectric block 45. The block is mounted to slide on the pins 46 whichare attached to the bracket 4l forming part of the abutment member 39.The springs 48 hold the block 45 and the contact 44 in projectedposition along the pins 46, as illustrated in Fig. 2.

When the abutment member 39 is actuated longitudinally of the guideways43, against tension of the springs 4|, the contact 49 is pushed intoengagement with the terminals 49, which closes electrical circuit acrossthe terminals, and thereby powers 'the machine. After contact 44 engagesthe terminals 49, the springs 48 are cornpressed during continued travelof the abutment member, the travel being limited by the length of theguideways 43. Compression of the springs 48 predetermines the force ofcontact of 44 across the terminals 49. When the abutment member 39 isreleased, the springs 4| actuate it to its forward inactive position,operating to open circuit r across the terminals 49 to therebydisconnect the power of motor I5.

Fig. 3 illustrates a wiring diagram for a bench grinder having twowheels which, according to conventional practice, are mounted atopposite ends of the common shaft |2, Fig. l. There is a line switch lfor each wheel l, operated to con'- nect the power source by loweringthe shield 3| of Fig. 1 to guard position. A light 34 for each wheel isin circuit with the switches I6, to be lit by either switch whenever itsincident shield 3| is lowered into guard position.

Each shield 3| also comprises a motor switch 38, which is located at thefront edge of the shield, as illustrated in Fig. l. When the shield 3|is lowered into guard position by the operator, its switch 38 occupies aposition in the path of the operator. When the operator stations himselfto operate the machine, the abutment member 39 is engaged by someportion of his body, for example by his torso, the engagement operatingto close the motor switch 38 incident to the wheel to be operated, thewheel being powered thereby. There are two motor switches 38 operable tocomplete the circuit of motor I5, the two switches 38 being availablefor alternative operation, depending upon which wheel the operatordesires to power and use.

By the present invention, the machine is incapable of being operateduntil and unless the shield 3| is lowered into guard positionillustrated in Fig. l, to close the line switch I. In this position ofthe shield 3| the operator is effectively guarded against being injuredby flying particles thrown from the machine. In addition, the motordrive of the machine is energized only when the operator has stationedhimself to use the machine for machining. Unless and until the operatorstations himself for operating the machine, the motor switch 3G is open.When the machine is in operation, if the operator is hurt, for exampleby inadvertently touching the wheel I, he naturally jumps away from themachine and opens the motor switch 38. This affords protection againstserious injury resulting from the machine continuing to run. The motorswitch 38 also operates to disconnect the motor drive automatically whenthe operator is not using the machine.

The specification and accompanying drawings disclose a structureconstituting a practical embodiment of the principles of the invention.The invention is not limited to the specific structure disclosed, thescope of the invention being determined by the accompanying claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

I claim:

l. In a safety device for a power-driven handoperated machine, a shieldmovable into guard position between the machine and the operator thereofand alternatively movable out of guard position, a power controlmechanism operable to connect a power source by the shield being movedinto guard position and alternatively operable to disconnect the powersource by the shield being moved out of guard position, the shield whenin guard position extending away from the machine and the outward edgethereof being then located for engagement by the body of the operatorstationed for operating the machine, an operating control mechanismmounted at the outward edge of the shield and being operable when theshield is in guard position to power the machine by the body of themachine operator pressing against it.

2. In a safety device as defined in claim 1, a light positioned toilluminate the machine, the power control mechanism operating to turnthe light on or off by the shield being moved respectively to and fromguard position.

in a safety device for an electric-motordriven hand-operated machine, ashield movable into guard position between the machine and the operatorthereof and alternatively movable out of guard position, a line switchfor the motor operable to closed position by the shield being moved intoguard position and alternatively operable to open position by the shieldbeing moved out of guard position, the shield when in guard positionextending away from the machine and the outward edge thereof being thenlocated for engagement by the body of the machine operator stationed tooperate the machine, an operating switch at the outward edge of theguard and being operated to closed position by the body of the machineoperator pressing against it.

4. In a safety device as defined in claim 3, all

5 electric light positioned to illuminate the machine, the light beingin circuit with the line switch to be turned on and 01T by the shieldbeing moved respectively to and from guard position.

5. In a safety device for an electric-motordriven bench grinder, ashield movable into guard position between the grinding wheel and themachine operator and alternatively movable out of guard position, a lineswitch for the motor operable to closed position by the shield beingmoved into guard position and alternatively operable to open conditionby the shield being moved out of guard position, the shield when inguard position extending away from the grinder and the outward edgethereof being then located for engagement by the body of the operatorstationed for operating the grinder, an operating switch at the outwardedge of the shield and being operated to respective closed and Aopenconditions by the 20 2,256,736

body of the machine operator being respectively REFERENCES CITED Thefollowing references are of record in the Yfile of this patent:

UNITED STATES PATENTS Number Name Date 1,220,620 Freeman Mar. 27, 19171,694,340 Weinland Dec. 4, 1928 1,979,457 Drum et al Nov. 6, 1934 EttenSept. 23, 1941 2,267,189 Braun Dec. 23, 1941

